1. Field of the Invention
This invention generally relates to a driving control system for a vehicle. More specifically, the present invention relates to a driving control system that automatically controls vehicle speed failsafe.
2. Background Information
Vehicle driving control systems generally include constant speed driving control systems or so-called xe2x80x9ccruise control systemsxe2x80x9d that automatically control the travel of a vehicle at a fixed speed designated by the driver. An example of such a driving control system will now be briefly explained. When the driver executes an operation such as depressing a brake pedal that closes a the set switch, the vehicle speed detected by a speed sensor at that instant is stored as the target value in a controller of a constant speed driving control unit. From then afterwards, the opening of an engine throttle valve is feedback-controlled in such a manner that an actual vehicle speed matches the target vehicle speed. A vacuum motor is coupled to the throttle valve to serve as an actuator for automatically controlling the throttle valve opening. The opening of the throttle valve is normally controlled by the operation of an accelerator pedal connected to throttle valve via a cable. However, during the constant speed driving control, the opening of throttle valve is controlled by the vacuum motor. More specifically, the controller varies the throttle position of the engine by using a control valve to regulate the operating vacuum pressure supplied to the vacuum motor.
The constant speed driving control executed by the controller is canceled when the driver manually releases the constant speed driving control, or when controller detects that the accelerator pedal or a brake pedal is being operated. Upon detecting such operation, the controller automatically cancels the constant speed driving control.
Since automatic cancellation induced by a braking operation is particularly important, a dual circuit is used as a failsafe measure. The dual circuit is provided with two switches that are connected in parallel. One of the switches is normally open, while the other switch is normally closed. When brake pedal is depressed, the normally open switch closes and the normally closed switch opens. The circuit containing the normally open switch is inputted to the controller. When the controller detects that the normally open switch is being closed due to a braking operation, the controller terminates the constant speed driving control.
Meanwhile, together with a self-holding relay the normally closed switch forms a power supply circuit for the control valve. When the set switch closes, the self-holding relay also closes and supplies current to the control valve. But when the brake pedal is operated, the normally closed switch opens. Accordingly, the self-holding relay opens and shuts off the current to the control valve, thus canceling the constant speed driving control. At this time, the self-holding state of the self-holding relay is also canceled. Therefore, the constant speed driving control remains canceled until the normally closed switch is closed and the set switch is operated again.
As described above, the conventional driving control system is provided with two switches that respond to braking operations. Consequently, even if, for example, the normally open switch becomes stuck in the closed state, the constant speed driving control can still be cancelled in a reliable fashion.
In contrast to conventional throttle control mechanisms that transmit the depression of the accelerator pedal to the throttle valve via a cable, the electronically controlled throttle devices that control the throttle opening using only an actuator have come to be utilized in vehicles of recent years. With an electronically controlled throttle device, the operation of the accelerator pedal is converted into an electric signal by a sensor. Accordingly, the controller controls the opening of the throttle valve by driving the actuator such as a step motor using this electric signal.
Therefore, such arrangement can provide the automated constant speed control similar to the conventional constant speed control by incorporating the constant speed control function into the controller. However, in such arrangement, the throttle opening is controlled solely through the actuator. Therefore, the current to the actuator cannot be shut off as a failsafe measure to cancel the constant speed control, since once the current to the actuator is shut off, the throttle valve cannot be controlled even manually. That means, the only available failsafe measure is to block a command to activate the constant speed control in a program within the central processing unit (CPU). However, this measure does not work if there is a problem with the input port of the central processing unit, because the program within the central processing unit will not recognize a braking operation in such situation. Accordingly, in the worst case scenario, the driver would not be able to cancel the driving control. As a possible remedy, the electronically controlled throttle device and the constant speed driving control device could be provided as completely separate controllers. Or, if the constant speed driving control function is incorporated into the electronically controlled throttle device, two central processing units could be utilized. However, neither of these remedies is realistic in view of the cost and the difficulties of installation into the vehicle.
In view of the above, there exists a need for vehicle driving control system, which overcomes the above-mentioned problems in the prior art. This invention addresses this need in the prior art as well as other needs, which will become apparent to those skilled in the art from this disclosure.
The object of the present invention is to provide a driving control system that achieves the failsafe function in a secure manner at a low cost. The aforementioned object can be attained by providing a vehicle driving control apparatus for a vehicle, comprising a vehicle speed detector, a braking detector, a driving force regulator, and a driving controller with a pulse signal generator and a logic circuit. The vehicle speed detector produces a speed signal indicative of an actual speed of the vehicle. The driving force regulator adjusts a driving force of the vehicle. The braking detector generates a braking signal indicative of a braking operation. The driving controller controls the driving force regulator so that the actual vehicle speed matches a prescribed target vehicle speed, and cancels control of the driving force regulator when the driving controller determines that a braking operation is being performed based on the braking signal from the braking detector. The pulse signal generator is configured to generate a pulse signal. The logic circuit is configured to receive the braking signal from the braking detector and the pulse signal from the pulse signal generator, such that the driving controller determines if a braking operation has been performed based on the pulse signal outputted from the logic circuit.
These and other objects, features, aspects and advantages of the present invention will become apparent to those skilled in the art from the following detailed description, which, taken in conjunction with the annexed drawings, discloses a preferred embodiment of the present invention.